Smart siting and passive design laid the groundwork, but to approach the couple’s goal of making a zero-energy house, Arkin Tilt selected an Altherma air-to-water heat pump system by Daikin. “The technology has been around for decades in Europe,” Tilt says, “but this is one of the first installed in California.” The device draws heat from the air outside and uses it to warm water both for domestic use and to power the in-floor radiant heating on the ground floor and in the upstairs bathroom. Best of all, the electricity the system uses is offset by 24 photovoltaic panels by Sanyo on the roof.